1. Field of the Invention
The present invention relates to a method of manufacturing a toner, as well as a toner.
2. Description of the Related Art
An electrophotographic image forming apparatus comprises an image forming process mechanism including: a photoreceptor; a charging section for charging a photoreceptor surface; an exposing section for irradiating with signal light the photoreceptor surface being charged, to form thereon an electrostatic latent image corresponding to image information; a developing section for supplying a toner contained in a developer to the electrostatic latent image formed on the photoreceptor surface, to form thereon a toner image; a transfer section provided with a transfer roller for transferring the toner image from the photoreceptor surface to a recording medium; a fixing section provided with a fixing roller for fixing the toner image onto the recording medium; and a cleaning section for cleaning the photoreceptor surface from which the toner image has been transferred. In the electrophotographic image forming apparatus, an image is formed by developing the electrostatic latent image by use of a one-component developer containing a toner or a two-component developer containing toner and carrier as a developer.
Through the electrophotographic image forming apparatus, an image of favorable image quality can be formed at high speed and low cost. This promotes the use of the electrophotographic image forming apparatus in a copier, a printer, a facsimile, or the like machine, resulting in a remarkable spread thereof in recent years. Simultaneously, the image forming apparatus has faced up to more demanding requirements. Among such requirements, particular attentions are directed to enhancement in definition and resolution, stabilization of image quality, and an increase in image forming speed, regarding an image being formed by the image forming apparatus. In order to fulfill these demands, a two-way approach is indispensable in view of both the image forming process and the developer. Regarding the enhancement in definition and resolution of the image, the reduction in diameter of toner particles is one of problems to be solved from the aspect of the developer. This is based on the perspective such that it is important to authentically reproduce the electrostatic latent image. As a method for obtaining a diameter-reduced toner, there has been developed a wet method in which a toner is manufactured in an organic solvent, water, or a combined solvent of organic solvent and water. A toner manufactured by the wet method is referred to as a chemical toner. Among the wet methods, a favorable method for obtaining a diameter-reduced toner exhibiting a narrow particle size distribution is an emulsification coagulation method in which resin particles and particles of other toner raw materials are coagulated and thus-obtained coagulated product is heated to manufacture a toner (refer to Japanese Unexamined Patent Publication JP-A 2001-228651, for example). However, resin represented by polyester, which is excellent in low-temperature fixing property and transparency and which is widely used as binder resin for toner, is hard to be granulated into fine particles. In order to granulate such resin into fine particles, it is necessary to use a detrimental organic solvent or a large amount of surfactant. The use of detrimental organic solvent should be avoided in consideration of environmental preservation, safety of operator, and the like. Further, the use of a large amount of surfactant makes it difficult to remove the surfactant after the manufacture of toner. Accordingly, in order to manufacture a diameter-reduced toner using polyester as binder resin by the emulsification coagulation method, polyester needs to be granulated into fine particles at the outset.
As a method of granulating the binder resin used for a toner into fine particles, there has been proposed a method including: a heating step of heating resin to a temperature of 100° C. or more at which a viscosity of the resin falls in an emulsifiable area of 100 Pa·s or less; and an emulsifying step of producing fine molten particles of the resin by giving a shearing force to an admixture of the resin heated at the heating step and a water-based solvent (refer to Japanese Unexamined Patent Publication JP-A 2004-189765, for example). According to an example of JP-A 2004-189765, there is obtained a water-based emulsion containing polyester particles of which volumetric average particle diameter is 1 μm or 800 nm. However, this is just a result obtained in a laboratory. If the method of JP-A 2004-189765 is applied to an industrial production of larger scale, it is very difficult to obtain a toner having a volumetric average particle diameter of 1 μm or less. Moreover, the particle diameter of resin particle obtained by the method is the volumetric average particle diameter and therefore, in practice, resin particles having a particle diameter exceeding 1 μm are contained. In the case where the resin particle having a particle diameter exceeding 1 μm is contained, a toner having a particle diameter exceeding 6.5 μm may possibly be generated in manufacture of toner according to the emulsification coagulation method.
Meanwhile, there has been proposed an emulsifying/dispersing apparatus comprising: an emulsifying/dispersing section for emulsifying/dispersing in a liquid serving as a matrix an emulsifying material which is granulated into fine particles; a leading passage for supplying a later-described multistage depressurization section with the pressurized emulsified liquid obtained by the emulsifying/dispersing section; a heat exchanging section disposed on the leading passage; and a multistage depressurization section for allowing the emulsified liquid supplied from the leading passage to have a reduced pressure causing no bubbling even if it is released to atmosphere, and then discharging the emulsified liquid (refer to International Publication WO03/059497, for example). In the emulsifying/dispersing apparatus, the emulsifying material is dispersed in a liquid under pressure, thereby preparing the emulsified liquid in which the emulsifying material is evenly dispersed. Next, the pressure on the emulsified liquid is reduced in a stepwise manner so that the final pressure is at a level causing no bubbling. By so doing, particles of the emulsifying material dispersed in the emulsified liquid are prevented from coarsening. The emulsifying/dispersing apparatus thus aims to obtain an emulsified liquid in which particles of emulsifying material having a uniform particle diameter are dispersed. By use of this emulsifying/dispersing apparatus which has the multistage depressurization section, a large shearing force can be given by the emulsifying/dispersing section, so that an emulsion of water/oil, for example, can be easily manufactured. However, on attempts to obtain a toner particle by use of this apparatus only, it is difficult to control the particle diameter, so that a desired toner particle with a reduced diameter cannot be obtained. Further, WO03/059497 has no disclosure about application of this emulsifying/dispersing apparatus to a manufacture of toner particles.